test: add import compliance tests

[JonathanOppenheimer]

Why this should be merged

This PR accomplishes three things:

1. Prevent files outside of graft/ directory from importing old, upstream geth files
   • Doing so violates the terms of the license and should absolutely be avoided.
2. Prevent files inside of the vms/evm directory from importing packages within the graft/ directory.
   • This is important because with the removal of coreth, there is not longer a natural boundary between the uplifted and non-uplifted code. We need to enforce such a boundary.
3. Add the EVM "libevm allowed import testing"
   • This is not quite as important because the test will exist within graft/* and be enforced, but moving it here will prevent the testing from being duplicated between coreth and subnet-evm
   • I also, frankly, added it because the import inspection code is practically identical, and I would have found it somewhat backwards to copy over the import inspection to code to what would be a 4th location.

How this works

The boundaries are as follows:

• graft/coreth can be imported everywhere in AvalancheGo except vms/evm.
  • However, vms/evm/emulate is an exception to this rule
• graft/subnet-evm can not be imported anywhere in AvalancheGo
  • However, vms/evm/emulate is an exception to this rule

How this was tested

Existing CI. I also added a sample "bad" commit (404acd5) to show how CI would behave.

edit: this is no longer a good example -- pretend the file is in vms/evm/sample_bad.go.

Need to be documented in RELEASES.md?

No

[JonathanOppenheimer]

See here for the source of the code below.

[JonathanOppenheimer]

I considered translating both of these files to .json to make the loading and parsing simpler in loadPatternFile().

However, the text files are very human readable and easy to maintain. Would like any opinions about the tradeoffs here!